1. Field of the Invention
This invention relates to accurate calibration and testing of anemometers which are located at remote places. These instruments over time may change in their readings because of deterioration and because of the lack of consistent periodic maintenance. It is necessary that a simple, reliable and portable apparatus be used for such field testing.
The accurate measurement of wind speeds, usually in remote places, is critical in predicting the behavior of forest and grass fires. Wind is the most significant variable among eleven that are used in fire rate-of-spread models. In an analysis and application of grass fuels data, it was found that a 17.5% wind speed error over the range of 13 to 30 miles per hour will result in a 40% error in predicted fire spread rates. Such high errors cannot be accepted when fires are being combatted. It is, therefore, vital to control of forest fires that a simple, reliable, portable and accurate means for periodically checking anemometers be used.
2. Description of the Prior Art
Because of the lack of a reliable calibration method, remote fire-weather stations have rarely checked their anemometers. In a few instances station observers have placed a new anemometer (usually not calibrated) next to the one in the field to check one against the others. This, however has proved inadequate because on a given day the range of natural wind speeds is limited, and tests over the range of 5 to 20 m.p.h. could not be made.
It has also been proposed to periodically test field units in wind tunnels. This is an expensive alternative and has been rejected.
Portable calibrators which rely upon centrifugal blowers have been used, but they are not compact.
Another method is the mounting of the anemometer to be tested upon the end of a long (6 feet) rotating boom. The wind speed measured is relative to the radial speed of the boom. This method is not portable and requires a large enclosed wind-free area for operation.